Neuropeptide FF (FLFQPQRF-NH2) was originally isolated from the bovine brain and found to have morphine modulating activity. Recently there are studies suggesting the involvement of neuropeptide FF (NPFF) in morphine abstinence and tolerance. In this study the role of endogenous NPFF in opiate dependence was further assessed using NPFF antibody as a specific antagonist. Rats, which were rendered dependent to opiate by morphine pellets, simultaneously received icv infusions of anti-NPFF IgG or control IgG. Naloxone induced abstinence signs were significantly lower in the group treated with anti-NPFF IgG than the group treated with control IgG. NPFF is highly localized in nerve terminals in the posterior pituitary. Superfusion of posterior lobes of rat pituitaries demonstrated that NPFF can be released from the pituitary by depolarizing concentration of KCI. Using this posterior pituitary as a model, we have found that naloxone can cause a significant release of NPFF from the pituitary of the rat pretreated with morphine. The amounts of NPFF released seem to increase with increasing dose and duration of the morphine treatment. The results strongly indicate that release of NPFF may participate in the naloxone precipitated opiate withdrawal. In order to further study the possible role of NPFF in opiate withdrawal and tolerance, work was initiated to attempt to isolate a specific cDNA clone for NPFF precursor protein. We are also currently isolating other NPFF-like peptides from adrenal and pancreatic glands with the aim of characterizing them both chemically and biologically.